System for injecting reactants in an exhaust line

ABSTRACT

A system to be fitted on an automotive vehicle for injecting reactants in an exhaust line of an engine of the vehicle includes a source of a liquid precursor of ammonia, a source of gaseous ammonia, an injection assembly designed to be fitted on the exhaust line and to inject liquid precursor and/or gaseous ammonia inside the exhaust line, the injection assembly including a single injector body to be fitted on the exhaust line, the injector body having a first inlet for the liquid precursor, a second inlet for the gaseous ammonia, and at least one outlet for injection inside the exhaust line.

BACKGROUND AND SUMMARY

The present invention relates to a system for injecting reactant(s) in an exhaust line of an engine. It may be used in the context of treating nitrogen oxides contained in exhaust gases flowing in an exhaust line of the engine, especially but not exclusively in a vehicle.

Exhaust gases formed due to the combustion of fuel in an internal combustion engine may contain a proportion of undesirable components, in particular nitrogen oxides (NOx).

Various exhaust after-treatment systems are known for removing or reducing the amount of undesirable components. Some of these systems require that at least one reactant fluid is injected in the exhaust line to react with the exhaust gases, either directly, or indirectly after having undergone one or several chemical transportation, and/or with the help of catalysts.

One known example of such an exhaust after-treatment system is the so-called selective catalytic reduction (SCR) system which has been implemented on various engine arrangements, including on-board of vehicles, for several years, in order to treat said nitrogen oxides and reduce air pollution. In such a system, exhaust gases, mixed with ammonia as a reducer, are treated in a specific catalytic converter where nitrogen oxides are converted into water and nitrogen which are both non-toxic substances.

In a first arrangement of the prior art, ammonia may be introduced in the exhaust line in the form of urea in aqueous solution from which ammonia is obtained through hydrolysis. The urea aqueous solution is a reactant which is in fact a precursor of the chemical species (ammonia) which will react with the NOx. It can be therefore qualified as indirect reactant, inasmuch as it contains inherently at least part of the chemical species which will react directly with the undesirable components. The urea solution is usually nebulised in the exhaust line to mix with exhaust gases upstream from the catalytic converter. To this end, a liquid urea injection nozzle is fitted on the exhaust line upstream from the catalytic converter. It has been proposed to use air assisted injectors for injecting the urea aqueous solution. Air assists in improving the quality of the injection spray, but air is not used as a reactant in the chemical reaction by which NOx are removed.

One problem with this type of exhaust gases treatment system is that, in some operating conditions of the engine, especially when the temperature of the exhaust gases is relatively low, for example around 20.0° C., urea, and/or it's the intermediate product in its transformation into ammonia, can crystallize before it has transformed into ammonia. In concrete terms, the aqueous solution of urea which is sprayed through the nozzle inside the exhaust pipe, according to a direction which may be angled with respect to the exhaust gases flow direction, may at least under certain circumstances tend to form a solid deposit inside the exhaust line, for example on the exhaust pipe wall, on the internal side thereof, for example opposite of the injection point. One consequence is that the cross section of the exhaust pipe may be progressively reduced, which may decrease the engine efficiency and which can seriously impair the engine operation in the long term. Also, this can lead to an improper treatment of the exhaust gases, leaving too much NOx.

In a second arrangement of the prior art, ammonia could be introduced in the exhaust line directly in the form of gaseous ammonia. In practice, there can be provided either a mere pressurized tank of ammonia or, preferably, one or several containers containing a solid on which ammonia has been previously absorbed or adsorbed. In use, gaseous ammonia can be released under certain operating conditions from the tank or from the container, and directed towards the exhaust line upstream from the catalytic converter. This implementation is advantageous in that it avoids crystallization that occurs when injecting liquid urea solution, and therefore provides good performance at relatively low temperatures. However, in practice, the containers need to be exchanged by the customer when all ammonia retained on the solid has been released, so as to meet legal requirements in terms of NOx emissions. This solution therefore proves inconvenient insofar as it requires frequent replacement of the containers and the corresponding infrastructure to handle and replace these containers.

US-2011/0219754 describes an exhaust gas purification apparatus where a gas additive and a liquid additive are supplied in an exhaust line. Two separate injection systems are provided, each having its own injector in the exhaust line. Such a system is expensive and is complicated to install, especially on a vehicle where available space is often scarce.

It therefore appears that, from several standpoints, there is room for improvement in systems for injecting reactant(s) in an exhaust line of an engine, especially in view of the treatment of nitrogen oxides contained in exhaust gases.

It is desirable to provide a system for injecting reactant(s) in an exhaust line of an engine, especially in view of treating nitrogen oxides contained in exhaust gases, that can overcome the drawbacks of the prior an.

More precisely, it is desirable to provide such a system which can be effective, even at low temperatures, which has an improved autonomy and which can be implemented on a vehicle without too much affecting the surrounding elements.

According to a first aspect, the invention relates to a system to be fitted on an automotive vehicle for injecting reactant(s) in an exhaust line of an engine, wherein the system comprises:

-   -   a source of a liquid precursor of ammonia;     -   a source of gaseous ammonia;     -   an injection assembly designed to be fitted on the exhaust line         and to inject liquid precursor and/or gaseous ammonia inside the         exhaust line, the injection assembly comprising a single         injector body to be fitted on the exhaust line, said injector         body having a first inlet for the liquid precursor, a second         inlet for the gaseous ammonia, and at least one outlet for         injection inside the exhaust line.

Thus, the system according to the invention provides two sources of reactant—either liquid or gaseous. Either or both reactant can be injected in the exhaust line, depending on the current conditions. The liquid reactant may be injected in liquid form and the gaseous reactant may be injected in gaseous form. As a result, the invention makes it possible to combine the advantages of the two sources and to limit their drawbacks.

Therefore, the system allows the efficient injection of a reducer at substantially any functioning point of the engine arrangement, in particular at substantially any temperature in the exhaust. Indeed, at relatively low temperatures, the liquid precursor can be replaced by gaseous ammonia, which prevents the formation of a solid deposit.

Furthermore, if one source has run out, the other one can be used. This ensures that the vehicle will run continuously while also respecting the legislation in terms of engine emissions.

Having a source of liquid precursor in addition to a source of gaseous ammonia ensures that the source of gaseous ammonia does not need to be replaced often. In other words, in addition to improving autonomy, this means that the vehicle driver will not be obliged to replace the source of gaseous ammonia himself in case of shortage of said source. In practice, the liquid precursor may be used as the usual reducer, while the gaseous ammonia may be used only at specific functioning points, when it is required to get enough efficiency. This allows saving the source of gaseous ammonia.

The reactants can be injected at different operating conditions of the engine, therefore at different times. Alternatively, the injected quantity of reducer at a given point in time can be increased by using simultaneously both sources, which means there is no need to develop high capacity systems for each source, while still matching the needed amount of reactant in particularly severe operating conditions of the engine were a high flow of ammonia is needed to efficiently remove NOx. On the other hand, the optimization of the usage of the two sources makes it possible either to extend the use of one of the sources, in particular the source of gaseous ammonia, and reduce the frequency of its replacement, or to downsize one of said sources.

Another advantage of the invention lies in the fact that the injector can be simplified since it is less demanding on the quality of the injection spray at some difficult functioning points. Indeed, since injection of liquid reactant can be avoided under non-optimal operating conditions, there is less of a need to have a perfectly nebulized spray. Moreover, in some embodiments of the invention, injecting simultaneously both the liquid precursor and gaseous ammonia at the same time can be sufficient to get a satisfactory quality of injection spray at said functioning points, especially at operation points where conditions are borderline with respect to the liquid reactant.

Furthermore, owing to the provision of a single injector body, the invention improves compactness and simplifies the system integration in a small allocated space. This further allows reducing the system overall cost, also because there can be provided a single protection package of the various components of the injector assembly, especially a single heat protection package. Said protection package can be fairly complicated and expensive due to the constraints resulting from the hot environment.

In practice, there may be provided one or several first inlets, as well as one or several second inlets. The first inlet(s) and second inlet(s) can be separate. Alternatively, there may be provided one or several common inlets for the liquid precursor and for gaseous ammonia.

According to an embodiment, the injector body can comprise one or several common outlets for the liquid precursor and the gaseous ammonia. In such a case, the flow path of the liquid precursor and the flow path of the gaseous ammonia inside the injector body have at least a common downstream portion. In case the first and second inlets are also common, the flow paths of liquid precursor and gaseous ammonia may be one and the same path over the whole length of the injector body.

According to another embodiment the first and second inlets can be separate, and the injector body can comprise at least one first outlet for the liquid precursor and at least one second outlet for the gaseous ammonia. In such a case, the first outlet(s) may be separate from the second outlet(s), the flow path of the liquid precursor and the flow path of the gaseous ammonia inside the injector body being separate. The flow path of the liquid precursor extends from the first inlet(s) to the first outlet(s), while the flow path of the gaseous ammonia extends from the second inlet(s) to the second outlet(s). In this embodiment, these flow paths are fully separate, meaning they have no common portion within the injector body. Such embodiments allow optimizing the flow path in the injector for each of the gas ammonia and of the fluid precursor. For example, the number, shape and/or direction of outlets can be optimized differently for the gas ammonia and for the fluid precursor.

The system may further comprise a flow control system for controlling the flow of liquid reactant and/or gaseous reactant, i.e for controlling the flow of liquid precursor or of gaseous ammonia to be injected by the injection assembly. Owing to this flow control system, it can be decided to inject in the exhaust line either the liquid reactant or the gaseous reactant or both, depending on the current conditions.

Typically, the flow control system can comprise at least one dosing device for dosing the liquid precursor and/or the gaseous ammonia to be injected inside the exhaust line.

According to several implementations of the invention, which can be combined:

-   -   one dosing device can be housed inside the injector body. Then,         the injector is not a simple nozzle but rather a controlled         injector. The dosing device can be the only dosing device of the         flow control system. Alternatively, there can be provided a         further dosing device outside the injector body, on either the         liquid circuit or the gas circuit or both, so that at least one         circuit is equipped with a double control arrangement. The         dosing device housed inside the injector body can be common to         both the liquid path and the gaseous path, or can be arranged on         only one of said paths. There may alternatively be provided two         separate dosing devices, each one arranged on one of said two         paths.     -   one dosing device can be located outside and upstream from the         injector body. In case no further dosing device is housed inside         the injector body, the injector is then a simple nozzle.     -   the flow control system can comprise one first dosing device         arranged on the liquid circuit extending from the source of the         liquid precursor of ammonia to the injector body and/or the flow         control system can comprise one second dosing device arranged on         the gas circuit extending from the source of gaseous ammonia to         the injector body. The first and second dosing devices can be         separate. Alternatively, the first and second dosing devices can         be one and the same device and can be arranged in a common         portion of the liquid circuit and the gas circuit, for example         at the connecting point between the liquid circuit and the gas         circuit.

The dosing device may comprise a controlled valve capable—of allowing all or part of the liquid precursor flow and/or all or part of the gaseous ammonia flow towards the injector body outlet(s), or of blocking said flow(s).

In a preferred but non limiting embodiment, the injection assembly is designed to be fitted on the exhaust line so as to be capable of injecting the liquid and/or the gaseous reactant inside the exhaust line upstream from a selective catalytic reduction device. Therefore, such system allows treating nitrogen oxides contained in exhaust gases flowing in the exhaust line.

According to a second aspect, the invention relates to an automotive vehicle equipped with a system as previously described.

These and other features and advantages will become apparent upon reading the following description in view of the drawing attached hereto representing, as non-limiting examples, embodiments of a system according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of several embodiments of the invention is better understood when read in conjunction with the appended drawings, it being however understood that the invention is not limited to the specific embodiments disclosed.

FIG. 1 is a schematic representation of a system according to the invention;

FIG. 2 is a detailed view of the injector of the system fitted on an exhaust line;

FIGS. 3 to 6 are longitudinal cross section views of several embodiments of the injector of the system according to the invention;

FIGS. 7 to 9 show several embodiments of the system of FIG. 1;

FIG. 10 is a schematic representation of the system of FIG. 1, according to a semi integrated embodiment.

DETAILED DESCRIPTION

FIG. 1 schematically shows a first embodiment of a system 1 for injecting reactant(s) in an exhaust line of an engine, especially in view of treating nitrogen oxides (NOx) contained in the exhaust gases produced by an automotive vehicle engine, especially by an internal combustion engine 3. The engine 3 may be a Diesel engine.

An exhaust line 2 carries exhaust gases from an engine 3 towards the atmosphere. In the exhaust line 2 is provided a selective catalytic reduction (SCR) device 4 in which NOx can be converted essentially into water and nitrogen by means of ammonia used as a reductant.

The system 1 basically comprises a double source of ammonia, namely a source 5 of a liquid precursor 6 of ammonia and a source 7 of gaseous ammonia 8, an injection assembly comprising an injector 10 fitted on the exhaust line 2 to inject liquid precursor and/or gaseous ammonia inside the exhaust line 2.

The injector 10 is preferably located on the exhaust line 2 upstream from the SCR device 4.

The system may comprise a flow control system for controlling the flow of liquid precursor and/or gaseous ammonia to be injected by the injector 10.

The source 5 of a liquid precursor 6 of ammonia comprises for example a tank 12 for storing said liquid precursor of ammonia, which is a substance that is chemically separable into gaseous ammonia and possible other components.

A liquid circuit 13 extending from the source 5 to the injector 10 carries the liquid precursor 6 up to the injector 10, which can inject said liquid precursor 6, still under liquid form, inside the exhaust line 2.

In practice, the precursor of ammonia can comprise an aqueous solution of urea 6 which may be nebulised in the exhaust gases through the injector 0. In the exhaust line 2, owing to the hot temperature of the exhaust gases, both an evaporation and an hydrolysis of the aqueous solution of urea may take place, resulting essentially in the production of gaseous ammonia, CO2 and water vapour. It should be noted that the liquid precursor of ammonia could be of a different chemical nature, for example aqueous ammonia.

The source 7 of gaseous ammonia 8 can comprise a unit including a container 14 containing a material 9 which, depending on the operating conditions, is capable of retaining gaseous ammonia in order to store it, and of releasing retained gaseous ammonia. For example, said material 9 can be capable of retaining gaseous ammonia by absorption and/or adsorption and/or formation of chemical complexes.

The material 9 can be solid. It can take several forms, including that of a powder, of granules or pellets, of open-cell foam, of a block, etc. Such type of source 7 has several advantages over conventional pressurized tanks containing gaseous ammonia:

-   -   the storage of ammonia is safe because the pressure level is         very low;     -   the amount ammonia which can be stored is quite important in a         limited volume, without having pressurized ammonia;     -   the gas which is stored is essentially pure ammonia which can be         easily dosed when released and injected in the exhaust line.

In an implementation, said material 9 can be capable of releasing retained gaseous ammonia above a threshold temperature. The unit can then further comprise a heater 15 capable of heating the material 9 above said threshold temperature, in order to provide gaseous ammonia 8 to the injector 10 when required. The heater 15 can be operated by the heat generated by the engine 3, either directly or indirectly. For example, the heater 5 could take advantage of the heat contained in exhaust gases, in an engine cooling fluid or in a lubrication fluid. The heater can also be independent of the heat produced by the engine, for example an electric heater

The range of temperatures at which the material 9 releases gaseous ammonia can be comprised between 100 and 140° C., with an optimum of for example around 120° C. Such a temperature is fairly high, which means that there is no need to cool—or excessively cool—the source 7 to maintain it in a low range of temperatures to allow gaseous ammonia 8 to be retained in the material 9, i.e. stored in the container 14. On the other hand, this release temperature is not too high, and therefore there is no need to excessively heat the material 9 to allow gaseous ammonia 8 to be released.

Examples of suitable materials include materials based on MgCl2, SrCl2 or CaCl2 and may include ammine complexes such as calcium ammine chloride Ca(NH3)8Cl2 or Strontium ammine chloride Ca(NH3)8Cl2. Suitable materials for retaining gaseous ammonia are described for example in U.S. Pat. No. 6,387,336 and WO-2006/012903, which can also be referred to for a description of suitable preparation processes.

Another possible form of gaseous ammonia source is described in U.S. Pat. No. 6,837,041.

Also, the gaseous ammonia source could comprise a pressurized tank of ammonia.

In any case, the fluid delivered by the source 7 of gaseous ammonia to the injector 10 may contain other gases in addition to gaseous ammonia. These additional gases could then be injected in the exhaust line 2 through the injector 10, together with the gaseous ammonia. These additional gases could be inert with respect to the chemical reaction occurring in the SCR device 4, or could be further reactants or catalysts.

This implementation of the source 7 of gaseous ammonia 8 is advantageous in that the invention provides two separate sources of reductant, which increases the system ability to deliver reactants in a suitable condition to the exhaust line under a wider range of operating conditions of the engine and exhaust arrangement.

A gas circuit 16 extending from the source 7 to the injector 10 carries the gaseous ammonia 8 up to the injector 10, which can inject said gaseous ammonia 8 inside the exhaust line 2.

According to the invention, the injector 10 comprises a single injector body 17 to be fitted on the exhaust line 2.

As shown in FIG. 2, there may be provided a single injection port 8 in the exhaust line 2, into which is inserted the injector body 17.

The injector body 17 is provided with:

-   -   at least one first inlet 21 for the liquid precursor 6, the         liquid circuit 13 being connected to said first inlet 21;     -   at least one second inlet 22 for the gaseous ammonia 8, the gas         circuit 16 being connected to said second inlet 22;     -   and at least one outlet 23 for injecting the reductant inside         the exhaust line 2.

The first and second inlets can be formed of one or several common inlets for both the gaseous ammonia and the liquid precursor. Alternatively, the first inlet and the second inlet can be separate, with then a possibility to have at least partly flow separate paths for the gaseous ammonia and the liquid precursor inside the injector.

As visible in FIG. 2, the injector body 17 may comprise an attachment portion, for attaching the body 17 to the exhaust line 2. The attachment portion 101 can be in the form of an external radially extending collar 101. The injector body 17 may also comprise a contact zone 102 in sealing contact with the exhaust line 2, where said contact zone ensure the gas tightness necessary to avoid any exit of the exhaust gases out of the exhaust line 2 at the interface between the injector body 7 and the exhaust line 2. The contact zone 102 can be formed on the attachment portion 101 or can be separate. This contact zone 102 demarcates an internal portion 103 of the injector body 7, which is received inside the exhaust line and may therefore be in contact with exhaust gases, and an external portion 104 which is not exposed to the exhaust gases. The first and second inlets 21 are preferably located on the external portion 104 of the injector body 17. The at least one outlet 23 is located on the internal portion 103 of the injector body. The injector body 17 may comprise several parts assembled together in a rigid assembly.

The flow control system 11 is provided in order to properly dose the quantity of ammonia to be introduced into the exhaust line 2, and more generally to properly dose and control the respective flows of liquid precursor 6 and gaseous ammonia 8.

The flow control system 1 can typically further comprise one or several of the following components (not shown), on the liquid circuit 13 and/or on the gas circuit 16: pumps, pressure regulators, sensors, actuators, filters, etc.

The flow control system may comprise at least one dosing device 24 for dosing the liquid precursor 6 and/or the gaseous ammonia 8 to be injected inside the exhaust line 2.

Advantageously, the flow control system 11 can further comprise a control unit 25 for controlling the dosing device(s) 24 according to at least one operational parameter, such as the current engine conditions, the measured or estimated current quantity of NOx in the exhaust gases, the temperature of exhaust gases, the remaining quantity of liquid precursor 6 in the source 5 and/or the remaining quantity of gaseous ammonia 8 in the source 7. The control unit 25 can further control other components of the flow control system 11, as well as the heater 15.

It has to be noted that the illustration of the system 1 in FIG. 1 is schematic and should not be considered as limitative.

For example, on the one hand, other embodiments of the flow control system 11 could be envisaged. Thus, although the flow control system 11 is shown as being fully outside the injector 10, part of said system 11 could be included in the injector 10, such as for example at least one dosing device 24. Besides, although two separate dosing devices 24 have been illustrated, one on the liquid circuit 13 and one on the gas circuit 16, there could be provided a single common dosing device 24, or only one dosing device 24 either on the liquid circuit 13 or on the gas circuit 16.

On the other hand, the illustrated injector 10 comprises two separate inlets 21,22 and a single outlet 23, but other implementations could be envisaged. For example, the injector body 17 could be provided with a single inlet for both the liquid precursor 6 and the gaseous ammonia 8, the liquid circuit 13 and the gas circuit 16 merging upstream from the injector 10. Some possible implementations will be described with reference to FIGS. 3 to 6.

In the embodiment shown in FIG. 3, the injector 10 comprises one common outlet 23 for the liquid precursor 6 and the gaseous ammonia 8. As a result, the flow path of the liquid precursor 6, from the first inlet 21 to the outlet 23, and the flow path of the gaseous ammonia 8, from the second inlet 22 to the outlet 23, inside the injector body 17, have a common downstream portion. In this illustrated embodiment, the injector 10 is provided with a single first inlet 21 and a single separate second inlet 22, but other implementations could be envisaged. Also several common outlets could be provided.

With this embodiment, it may be necessary, for example for reasons relating to pressure, to empty the injector body 17, before injecting gaseous ammonia, by purging the liquid circuit 13 up to a point located upstream from the injector 10. This could for example be achieved by means of a pump of the liquid circuit 13.

In the embodiment shown in FIG. 4, the injector 10 comprises one first inlet 21 and one second inlet 22 which are separate. Furthermore, the injector 10 comprises at least one first outlet 23 a for the liquid precursor 6 and at least one second outlet 23 b for the gaseous ammonia 8, the first outlet(s) being separate from the second outlet(s). Therefore, the flow path of the liquid precursor 6, from the first inlet 21 to the first outlet 23 a, and the flow path of the gaseous ammonia 8, from the second inlet 22 to the second outlet 23 b, inside the injector body 17, are separate. In other words the first inlet is fluidically connected only to the first outlet(s), forming a flow path for only the liquid precursor, and the second inlet is fluidically connected only to the second outlet(s), forming a flow path for only the gaseous ammonia.

For example, the injector body may have a substantially central duct 26 extending from the first inlet 21 to the first outlet 23 a, in which the liquid precursor 6 can flow. Besides, the gaseous ammonia 8 can flow in an annular chamber 27 formed between the duct 26 and a peripheral wall of the injector body 17 and exit the injector 10 through either a single annular second outlet 23 b or several second outlets 23 b, for example circular outlets arranged along a ring. In other words, in this embodiment, the first and second outlet(s) are arranged concentrically one to the other. Preferably, the second outlet(s) for the gaseous ammonia are arranged concentrically around the first outlet(s) for the liquid precursor. Nevertheless, the first and second outlets could also be arranged differently, for example side by side.

Also, the first and second outlet(s) may be are arranged as in this embodiment so as to direct their respective fluids along the same direction in the exhaust line. Alternatively, the injection directions could be different between the first outlet(s) and the second outlet(s). In case the first and/or the second outlets are formed of several outlets, each of those respective first and second outlets could be arranged to inject the corresponding fluid in several directions.

The injectors 10 shown in FIGS. 3 and 4 are devoid of any internal dosing device, and are thus simple nozzles.

On the contrary, the injector 10 may be a controlled injector, i.e. can comprise at least one dosing device housed inside the injector body 17. Said dosing device can comprise a controlled valve capable of allowing all or part of the liquid precursor flow and/or all or part of the gaseous ammonia flow towards the exhaust line 2, or of blocking said flow(s). The controlled valve may be proportional or of the on/off type.

The injector 10 depicted in FIG. 5 is similar to the one depicted in FIG. 3, and would encompass any of its variants, but further includes a dosing device 24 housed in the common downstream portion of the liquid precursor and gaseous ammonia paths. Said dosing device 24 may comprise a needle 28 pushed downstream by a spring 29 in order to close the outlet 23. It can be an electromagnetically controlled dosing device, for example by means of a coil 30 provided on the injector body 17 and a magnet or armature 31 provided on the needle 28, in a facing relationship with the coil 30. The needle 28 can be moved upstream, despite the effort exerted by the spring 29, in order to free the outlet 23, upon an appropriate action of the flow control system 11. The injector 10 thus makes it possible to dose the global flow of liquid precursor 6 and gaseous ammonia 8 inside the injector body 17. Dosing separately the liquid precursor 6 and gaseous ammonia 8 would require a further dosing device outside and upstream from the injector 10. The dosing device could alternatively be pneumatically or hydraulically controlled.

The injector 10 depicted in FIG. 6 is similar to the one depicted in FIG. 4 or any of its variants, in that it has a fully separate flow path for the liquid precursor and for the gaseous ammonia inside the injector body, but it further includes a dosing device 24 housed inside the injector body 17. The dosing device 24 is here arranged on the liquid precursor path, i.e. inside the duct 26. Therefore, it can only be used to dose the liquid precursor flow, but not the gaseous ammonia flow. Alternatively, the dosing device 24 could be arranged on gaseous ammonia path to dose the gaseous ammonia flow, but not the liquid precursor flow. The dosing device 24 may be similar to the dosing devices described with reference to FIG. 5: it may include a needle 28 pushed downstream by a spring 29 in order to close the outlet 23, as well as a coil 30 and a magnet or armature 31 for moving the needle 28 upstream in order to open the outlet 23 a.

Further variants of the embodiments of FIG. 5 or 6 would include a dosing device in a flow path having several outlets.

In further variants, the injector body could comprise fully separate flow paths for the liquid precursor and for the gaseous ammonia inside the injector body, and the injector could comprise a dosing device in each of said flow paths.

Having a dosing device in the injector body may make it easier to control with precision the amount of the corresponding fluid which is really injected in the exhaust line.

Several embodiments of the system 1 according to the invention are shown in FIGS. 7 to 9.

According to a first embodiment, depicted in FIG. 7, the flow control system 11 comprises one first dosing device 24 a arranged on the liquid circuit 13, and one second dosing device 24 b arranged on the gas circuit 16, the first and second dosing devices 24 a, 24 b being separate. In practice, the dosing device 24 a, 24 b can comprise each a two way valve capable of directing all or part of the corresponding flow towards the injector 10 or of blocking said flow. The injector 10 can be either a simple nozzle or a controlled injector, in order to provide a further control of the flows. The liquid precursor and gaseous ammonia can be introduced jointly, via a same inlet, or separately, via inlets 21,22, in the injector 10. Besides, the liquid precursor and gaseous ammonia paths inside the injector 10 can be fully separate or have at least one common portion.

This embodiment is advantageous in that it provides a maximum flexibility of the system 1, insofar as each source 5, 7 is equipped with its own flow control arrangement. Moreover, it makes it possible to install some components of the flow control system 11, especially some more fragile components such as electric or electronic components, in a more favourable area, for example further away from the environment of the exhaust line 2 which is hot and subject to vibrations.

According to a second embodiment, depicted in FIG. 8, the liquid circuit 13 and the gas circuit 16 merge upstream from the injector 10, which therefore may have a common inlet for both the gaseous ammonia and the liquid precursor. A common dosing device 24 c can be arranged at the connecting point between these circuits 13, 16 to let the appropriate reductant, or the appropriate mixture of both reductants, flow towards the injector 10. The dosing device 24 c can comprise a three position valve, but this implementation is not limitative. Additional components of the flow control system 11 can also be provided on the corresponding circuits 13, 16. In this embodiment, the injector 10 is preferably a controlled injector 10.

This embodiment is advantageous in that it can be fairly inexpensive insofar as a single dosing device 24 c may be provided.

According to a third embodiment, depicted in FIG. 9, the system 1 can further comprise an air line 35 for carrying pressurized air 36 towards an inlet of the injector body 17, in order to assist the injection of the liquid precursor 6. The injector body could include a dedicated air inlet.

In practice, the air line 35 can be fluidically connected to the gas circuit 16, upstream from the injector 0. A valve 37 may be arranged at the connecting point of the air line 35 and the gas circuit 16 to direct either gaseous ammonia 8 or air 36 towards the injector 10. Air 36 can come from an air source of the vehicle or can be generated by an external source, such as a mechanical or electrical air pump.

The embodiment of FIG. 9, with an additional air line 35 is preferably implemented with an injector comprising fully separate flow paths for the liquid precursor and for the gaseous ammonia inside the injector body, such as one of the injectors shown on FIG. 4 or 6 or any of their variants.

Depending on the position of the valve 37, the system 1 can be operated in at least two different modes:

-   -   in a first operation mode of the system, gaseous ammonia 8 can         be injected inside the exhaust line 2, through the gas circuit 6         and the gas path inside the injector body 17;     -   in a second operation mode of the system 1, both liquid         precursor 6 and air 36 are introduced in the injector 10 to be         injected in the exhaust line 2. Air 36 improves the quality of         the liquid precursor spray, thereby improving the system         efficiency. Inside the injector 10, air 36 can flow along the         gaseous ammonia path.

Of course, this system, as well as other systems as above, can also be operated in way such that liquid precursor and ammonia gas are injected simultaneously.

As shown in FIG. 10, the system could also be arranged according to a semi integrated embodiment.

For example, the tank 2 for storing the liquid precursor 6 and the container 14 for storing gaseous ammonia could be juxtaposed in a same supply unit 38. Alternatively, the container 14 for storing gaseous ammonia could be located inside the tank 12 for storing the liquid precursor 6. In addition, or alternatively, the flow control system 11 can be fully housed in a control box 39, i.e. a box receiving all the components of the flow control system 11.

Such a semi integrated embodiment is advantageous in terms of compactness and ease of implementation.

The invention is of course not limited to the embodiments described above as examples, but encompasses all technical equivalents and alternatives of the means described as well as combinations thereof. 

1. A system to be fitted on an automotive vehicle for injecting reactant(s) in an exhaust line of an engine of the vehicle, wherein the system comprises: a source of a liquid precursor of ammonia; a source of gaseous ammonia; an injection assembly designed to be fitted on the exhaust line and to inject liquid precursor and/or gaseous ammonia inside the exhaust line, the injection assembly comprising a single injector body to be fitted on the exhaust line, the injector body having a first inlet for the liquid precursor, a second inlet for the gaseous ammonia, and at least one outlet for injection inside the exhaust line.
 2. The system according to claim 1, wherein the injector body comprises one or several common outlets for the liquid precursor and the gaseous ammonia, the flow path of the liquid precursor and the flow path of the gaseous ammonia inside the injector body having at least a common downstream portion.
 3. The system according to claim 1, wherein the first and second inlets (21, 22) are separate and in that the injector body comprises at least one first outlet for the liquid precursor and at least one second outlet for the gaseous ammonia, the first outlet(s) being separate from the second outlet(s), the flow path of the liquid precursor and the flow path of the gaseous ammonia inside the injector body being separate.
 4. The system according to claim 1, wherein it further comprises a flow control system for controlling the flow of liquid precursor and/or gaseous ammonia to be injected by the injection assembly.
 5. The system according to claim 4, wherein the flow control system (11) comprises at least one dosing device for dosing the liquid precursor and/or the gaseous ammonia to be injected inside the exhaust line.
 6. The system according to claim 5, wherein one dosing device is housed inside the injector body.
 7. The system according to claim 5, wherein one dosing device is located outside and upstream from the injector body.
 8. The system according to claim 5, wherein the flow control system comprises one first dosing device (24 a) arranged on the liquid circuit extending from the source of the liquid precursor of ammonia to the injector body.
 9. The system according to claim 5, wherein the flow control system comprises one second dosing device arranged on the gas circuit extending from the source of gaseous ammonia to the injector body.
 10. The system according to claim 8, wherein the flow control system comprises one second dosing device arranged on the gas circuit extending from the source of gaseous ammonia to the injector body, and the first and second dosing devices are separate.
 11. The system according to claim 8, wherein the flow control system comprises one second dosing device arranged on the gas circuit extending from the source of gaseous ammonia to the injector body the first and second dosing devices are one and the same device and are arranged in a common portion of the liquid circuit and the gas circuit.
 12. The system according to claim 5, wherein the dosing device comprises a controlled valve capable of allowing all or part of the liquid precursor flow and/or all or part of the gaseous ammonia flow towards the injector body outlet(s), or of blocking the flow(s).
 13. The system according to claim 5, wherein the flow control system comprises a control unit for controlling the dosing device(s) according to at least one operational parameter.
 14. The system according to claim 1, wherein it further comprises an air line for carrying air towards an inlet of the injector body in order to assist the injection of the liquid precursor.
 15. The system according to claim 13, wherein the air line is fluidically connected to a gas circuit (16), which extends from the source of gaseous ammonia to the injector body.
 16. The system according to claim 1, wherein the injection assembly is designed to be fitted on the exhaust line so as to be capable of injecting liquid precursor and/or gaseous ammonia inside the exhaust line upstream from a selective catalytic reduction device, the system therefore allowing treating nitrogen oxides contained in exhaust gases flowing in the exhaust line.
 17. The system according to claim 16, wherein the source of gaseous ammonia comprises a unit including a container containing a material which, depending on the operating conditions, is capable of retaining gaseous ammonia in order to store it, and of releasing retained gaseous ammonia.
 18. The system according to claim 17, wherein the material contained in the unit is capable of retaining gaseous ammonia by absorption and/or adsorption and/or formation of chemical complexes.
 19. The system according to claim 17, wherein the material contained in the unit is capable of releasing retained gaseous ammonia above a threshold temperature, and in that the unit further comprises a heater capable of heating the material above the threshold temperature.
 20. The system according to claim 1, wherein the liquid precursor of ammonia comprises an aqueous solution of urea.
 21. The system according to claim 1, wherein it comprises a tank (12) for storing the liquid precursor and a container for storing gaseous ammonia, the tank (12) and the container being juxtaposed in a same supply unit (38).
 22. The system according to claim 4, wherein the flow control system is fully housed in a control box (39).
 23. An automotive vehicle equipped with a system according to claim
 1. 